This study of membrane transport is targeted to provide the basic scientific information needed to understand the mechanisms whereby age-dependent perturbations in physiological control systems lead to the inability of the organism to maintain homeostasis. Membrane vesicles derived from the luminal brush border segment and the peritubular basal-lateral region of the renal tubule epithelial cell plasma membrane are used as model systems. Topics investigated include: 1) the role of the membrane potential in the Na ion gradient-dependent uptake of D-glucose by brush border membrane vesicles; 2) the mechanisms and specificities of amino acid transport systems; 3) the uptake systems for Na ion, Na ion-H ion, Na ion-Na ion, and Na ion-K ion exchanges; 4) the development of methods for the isolation and the characterization of the basal-lateral region of the renal tubule plasma membrane; 5) the comparison of the mechanism by which solutes enter and exit the tubular epithelial cell.